The present invention relates to thermally stimulating a mechanically-lifted well by concurrently generating heat and nitrogen in or near the openings into the reservoir, while mechanically lifting liquid from the well. More particularly, the invention relates to an economical process by which such a treatment can be accomplished with relatively little equipment or down-time where the production of fluid from a well is undesirably slow in response to an artificial lifting of liquid.
Numerous procedures have been previously suggested for heating and/or dissolving plugging materials which may have been accumulated in or near the openings between the borehole of a well and the pores of a subterranean reservoir. U.S. Pat. No. 2,228,629 suggests dropping into a well borehole a silk or wool container filled with oil-coated particles of aluminum and flaked caustic soda, so that those materials will react when the fabric container is ruptured within the brine in the borehole. U.S. Pat. No. 2,799,342 suggests injecting an oil solvent dispersion of alkali metal particles (smaller than about 5 microns) into an aqueous liquid within the borehole. U.S. Pat. No. 2,889,884 suggests injecting into the reservoir a non-aqueous solvent solution of metal hydrides which are exothermically reactive with water. U.S. Pat. No. 3,279,514 suggests separately injecting fluids containing an oil solvent, water, and a liquid dispersion of a salt or hydroxide which reacts exothermically with water, so that the fluids mix and react. U.S. Pat. Nos. 3,342,264 and 3,342,265 suggest sequentially injecting compositions containing triglyceride oils (such as lecithin) an aqueous alkali, and then flushing the boreholes with water to remove such passageway plugging materials. U.S. Pat. No. 3,914,132 suggests injecting a solvent mixture of aromatic hydrocarbon and amine as an oil solvent which is capable of dissolving any contacted asphaltenic solids.
In the course of research relating to other well treating problems, it has been found that certain self-reactive aqueous solutions could be compounded and flowed into wells with their components arranged to subsequently react to yield nitrogen gas and heat at times and rates which were useful for various well treating processes. Such discoveries have been described in the following U. S. patents and patent applications.
U.S. Pat. No. 4,178,993 and its U.S. Pat. No. 30,935, by E. A. Richardson and R. F. Scheuerman describe a process for initiating fluid production from a liquid-containing well by injecting an aqueous solution containing nitrogen-gas-generating reactants having a concentration and rate of reaction correlated with the pressure and volume properties of the reservoir and the well conduits to react at a moderate rate within the well and/or the reservoir to generate enough gas to displace sufficient liquid from the well to reduce the hydrostatic pressure within the well to less than the fluid pressure within the reservoir.
U.S. Pat. No. 4,219,083 by E. A. Richardson and R. F. Scheuerman describes a process for cleaning well casing perforations by injecting an aqueous solution containing nitrogen-gas-generating reactants, an alkaline buffer providing a reaction-retarding pH and an acid-yielding reactant for subsequently overriding the buffer and lowering the pH in order to trigger a fast-rising pulse of heat and pressure which causes a perforation-cleaning backsurge of fluid through the perforations.
U.S. Pat. No. 4,232,741 by E. A. Richardson, R. F. Scheuerman, D. C. Berkshire, J. Reisberg and J. H. Lybarger describes a process for temporarily plugging thief zones within a reservoir by injecting an aqueous solution containing nitrogen-gas-generating reactants, a foaming surfactant, an alkaline buffer and an acid-yielding reactant, arranged so that they initially delay the reaction and subsequently initiate a moderate rate of gas production, in order to form a foam which is, temporarily, relatively immobile within the reservoir formation.
Patent application Ser. No. 200,176 filed Oct. 24, 1980, by D. R. Davies and E. A. Richardson now U.S. Pat. No. 4,410,041 describes a process for conducting a production test by circulating a solution of nitrogen-gas-generating reactants within conduits within a well, with the solution buffered at a pH providing a promptly-initiated reaction having a relatively mild rate and being inflowed through a well conduit at a rate such that the gas being generated serves as a lift-gas for gas-lifting fluid from the reservoir through another well conduit.
U.S. Pat. No. 4,330,037, by E. A. Richardson and W. B. Fair, Jr. describes a process for treating an oil-containing reservoir in order to concurrently chemically heat the reservoir and increase its effective permeability to oil by injecting an aqueous solution of nitrogen gas-generating reactants which is arranged to have a volume, a rate of reaction and a heat-generating capability such that the heat-generation will occur below a selected depth and will cause a selected volume of the reservoir to be heated to a selected temperature.
The disclosures of the U.S. Pat. Nos. 4,178,933; 4,219,083, 4,232,741 and 4,330,037, and the patent applications Ser. Nos. 215,895 and 307,035 are incorporated herein by cross-reference.
Many things may cause a liquid-productive well to become less productive than desired. If the production rate is not sufficiently improved by artificially lifting enough liquid from the well borehole to provide a drawdown (or inflow pressure gradient from the reservoir to the borehole) which is substantially as high as can be provided by the reservoir pressure, or can be withstood by the materials in and around the borehole of the well, a relatively expensive remedial treatment may be needed. But, usually the well operator has little or no assurance that such a remedial treatment will significantly increase the productivity of the well. A primary object of the present invention is to provide a relatively inexpensive well treating process for determining whether the productivity of a poorly productive well (which may have been standing idle because of its low productivity) can be increased by a generation of heat and nitrogen gas, or a treatment with both the so-generated heat and gas and an oil-solvent or other fluid, in and around the openings into the reservoir.